Input detection and protection circuit

ABSTRACT

An input detection and protection circuit and an AC electronic ballast for HID lamps, including a power input circuit performing a first limitation to an input surge voltage and then performing a second limitation to a residual voltage from the first input surge voltage limitation; an input voltage acquisition circuit feeding back an input voltage to an MCU chip; a pull-in circuit for a relay connecting to a relay in the power input circuit; a PFC circuit, and an MCU chip controlling the PFC circuit to switch on and off according to voltage values input by the input voltage acquisition circuit, and controlling pull-in and drop-out of the relay through the pull-in circuit for the relay.

TECHNICAL FIELD

The present disclosure relates to the technical field of power supply,in particular to an input detection and protection circuit.

BACKGROUND

Development of power supply technology including electronic ballast, LEDdriver, power bank and the like has started many years ago, andapplications on such technology are becoming more and more mature,especially in agriculture and in energy-saving renovation of street lamprecently. The differences in diversified demands of the market havepromoted a huge product family, with a wide variety of products, acommon power ranges from 70 W to 1000 W, and common voltages including120 V, 208 V, 220 V, 230 V, 240 V, 277 V, 347 V, 380 V, 400 V, 480 V,etc. due to different standards of voltages in different countries. Itis not hard to see from the above voltage specifications that the powerdistribution environments where various power supplies locate could becomplex, so attention must be paid to the rated voltage range ofproducts and the environments of grid during installation.

To be further understood, the use environment can be divided intohousehold use at single voltage, medium-scale power supply to motors,and grid distribution in large-scale industrial applications. Therefore,the voltage environments of the grid are complex. When In use, an inputsurge voltage is monitored to reach several kilovolts, and thefluctuation and instability of the grid reach more than 30% when, farexceeding the designed withstand voltage of products, thus the maincause for failures is such rugged grid environments. According tofailure analysis, there are several main causes as follows for a largenumber of damages:

One cause is the misuse of two live wires in the 3-phase 4-wire powerdistribution, where the actual input voltage is 1.7 times the nominalvalue. For example, when a product with a nominal rated voltage of 230 Vis connected to a wrong wire, it has a voltage of up to 400 VAC, whichgreatly exceeds a withstand voltage thereof. A second cause is that thegrid has a voltage surge exceeding the withstand voltage of internaldevices of the product, due to its instability of the grid, resulting indamage to electrolytic capacitors and MOS transistors. A third cause isthe three-phase imbalance caused by neutral line phase loss, where onephase voltage exceeds an input rating, resulting in damage to internalelectrolytic capacitors and MOS transistors. A fourth cause is a surgevoltage induced at the moment of lightning or of switching on. A fifthcause is a rapid change of high current when the input capacitor ischarged, which results in an induced high voltage generated when thecurrent reduces.

After an observation of a long-term usage, it can be found that thedamage caused by abnormal input voltage accounts for more than 60% ofall failure rates, wherein the failure rate in the household useenvironment is obviously lower than that in industrial applicationssince there is no multiple service voltages in the household useenvironment. The failure rate in the usages of motor is significantlyhigher than that in the usages of grid. The probability of damage at themoment of switching on and off is greater than that in normal operation,and the failure rate in the thunderstorm weather is higher than that inthe sunny weather.

Therefore, the present disclosure proposes improvements in view of theabove problems.

SUMMARY

The present disclosure aims to provide an input detection and protectioncircuit as improvements with respect to the prior arts.

In order to address the above issues, a technical scheme according tothe present disclosure is provided as follows:

An input detection and protection circuit, wherein the input detectionand protection circuit includes a power input circuit, an input voltageacquisition circuit, a pull-in circuit for a relay, a PFC circuit and anMCU chip.

The power input circuit performs a first limitation to an input surgevoltage, and then performs a second limitation to a residual voltagefrom the first input surge voltage limitation; the input voltageacquisition circuit feeds back an input voltage to the MCU chip, thepull-in circuit for a relay is connected to a relay in the power inputcircuit, and the MCU chip controls the PFC circuit to switch on and offaccording to voltage values input by the input voltage acquisitioncircuit, and controls pull-in and drop-out of the relay through thepull-in circuit for the relay.

As an improvement of the input detection and protection circuitaccording to the present disclosure, the power input circuit includes: afirst varistor, a second varistor, a thermistor and the relay, and theinput surge voltage is firstly limited by the first varistor and thensecondly limited by the second varistor and the thermistor.

As an improvement of the input detection and protection circuitaccording to the present disclosure, the power input circuit furtherincludes a third varistor connected in parallel to both ends of thethermistor.

As an improvement of the input detection and protection circuitaccording to the present disclosure, the input voltage acquisitioncircuit includes:

a first diode, a second diode, a first capacitor, a second capacitor, afirst resistor and a second resistor; one end of each of the first andsecond diodes is connected to the power input circuit and the other endthereof is connected to the MCU chip through the first and secondcapacitors and the first and second resistors.

As an improvement of the input detection and protection circuitaccording to the present disclosure, when the input voltage is within asafe range, the MCU chip controls the pull-in of the relay through thepull-in circuit for the relay, and when the input voltage is out of thesafe range, the relay is dropped-out.

As an improvement of the input detection and protection circuitaccording to the present disclosure, the input voltage acquisitioncircuit includes: a third resistor, a fourth resistor and a thirdcapacitor; one end of the third capacitor is connected to the PFCcircuit and the other end thereof is connected to the MCU chip throughthe third resistor and the third capacitor.

As an improvement of the input detection and protection circuitaccording to the present disclosure, when the input voltage is within asafe range, the MCU chip controls the PFC circuit to be switched on; andwhen the input voltage is out the safe range, the MCU chip controls thePFC circuit to be switched off.

As an improvement of the input detection and protection circuitaccording to the present disclosure, the pull-in circuit for the relayincludes a triode, a fifth resistor, a sixth resistor and a fourthcapacitor, a collector of the triode is connected to the relay, and thecollector and an emitter of the triode are electrically connected to theMCU chip through the fifth resistor, the sixth resistor and the fourthcapacitor.

As an improvement of the input detection and protection circuitaccording to the present disclosure, the input detection and protectioncircuit further includes a power supply module that supplies power tothe relay and the MCU chip.

As compared with existing technologies, the present disclosure hasbeneficial effects that the input detection and protection circuitaccording to the present disclosure can provide protection againstabnormalities due to extremely high input voltage, such as phase lossfrom the grid, incorrect wire connection during installation, high surgevoltage at the moment of switching on, impulses by continuous lightning.According to the present disclosure, the input detection and protectioncircuit acquires a charging voltage of a capacitor of a subsequentstage, and enables the pull-in of the relay according to the internalsetting in order to effectively reduce surge current and impact.Meanwhile, the input detection and protection circuit monitors the inputvoltage, such that protection can be provided when the voltage isextremely high or low, wherein the relay can be dropped-out in case ofan abnormality, and a standby current can be provided to the MCU by PTCto indicate such abnormality.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better illustrate embodiments of the present disclosure ortechnologies in the prior art, the accompanying drawings to be used inthe embodiments or existing technologies will be briefly describedbelow. Obviously, the drawings in the following description are only apart of embodiments described in the present disclosure, and a person ofordinary skill in the art may also obtain other drawings based on thesedrawings without creative effort.

FIG. 1A is a first portion of a circuit diagram of an embodiment of aninput detection and protection circuit according to the presentdisclosure; and

FIG. 1B is a second portion of the circuit diagram of the embodiment ofthe input detection and protection circuit.

DETAILED DESCRIPTION

The technical schemes in the embodiments of the present disclosure willbe clearly and completely described as below with reference to theaccompanying drawings in the embodiments of the present disclosure.Obviously, the described embodiments are only a part of, not all of, theembodiments of the present disclosure. All other embodiments obtained bya person of ordinary skill in the art based on the embodiments of thepresent disclosure without creative effort shall fall into theprotection scope of the present disclosure.

As shown in FIG. 1A and continued on FIG. 1B, an input detection andprotection circuit according to the present disclosure is provided forinput detection, wherein the input detection and protection circuitincludes a power input circuit 1, an input voltage acquisition circuit2, a pull-in circuit 3 for a relay, a PFC circuit 4 and an MCU chip 5.Lines A5, A4, A3, A2, and A1 shown in FIG. 1A are in connection withlines B5, B4, B3, B2, and B1, respectively, shown in FIG. 1B.

The power input circuit 1 is configured to limit an input surge voltagefor the first time and then limit the residual voltage for the secondtime after that. Specifically, the power input circuit 1 includes: afirst varistor ZR1, a second varistor ZR2, a thermistor PTC and a relayK1. The input surge voltage is limited by the first varistor ZR1, andthen by the second varistor ZR2 and the thermistor PTC. The power inputcircuit 1 further includes: a third varistor ZR3 which is connected inparallel to both ends of the thermistor PTC and configured to protectthe thermistor PTC.

Therefore, when the input voltage is too high, the thermistor PTC andthe second varistor ZR2 in the circuit will limit such voltage, thethermistor PTC exhibits a high impedance, the voltage is controlled at asafe value by the second varistor ZR2, the voltage endurance capabilityof the thermistor PTC is above 300 VAC and exhibits a high impedanceduring overcurrent. When an input stage voltage is higher than alimiting voltage of the second varistor ZR2, the residual voltage isapplied to the thermistor PTC to realize enhanced protection for asubsequent stage of the circuit. In case of phase loss during input, theinput voltage will be 1.73 times the rated voltage. Taking a voltage of230 V as an example, in case of the most serious phase loss, a rectifiedvoltage will ranges from 550 V to 600 V, while electrolytic capacitorsof a subsequent stage are generally DC electrolytic capacitors of 450 to500 V, thus resulting in overvoltage damage to the electrolyticcapacitors. Therefore, the power input circuit 1 can effectively preventdamage to devices.

The input voltage acquisition circuit 2 feeds back the input voltage tothe MCU chip 5. Specifically, the input voltage acquisition circuit 2includes: a first diode D1, a second diode D2, a first capacitor C6, asecond capacitor C7, a first resistor R3 and a second resistor R4,wherein one end of the first diode D1 and one end of the second diode D2is respectively connected to the power input circuit 1, and the otherend thereof is respectively connected to the MCU chip 5 through thefirst capacitor C6, the second capacitor C7, the first resistor R3 andthe second resistor R4.

In this case, the MCU chip 5 determines whether to pull-in the relay K1according to the value of the input voltage. Relay K1 is not to bepulled-in when such value exceeds a safe value of the circuit, and thevoltage will then be limited within a safe range by the second varistorZR2 and the thermistor PTC. After the input voltage falls within thesafe range, the MCU chip 5 calculates a reasonable delay pull-in timeaccording to the voltage applied on the electrolytic capacitor, andcontrols a surge current at a possibly lowest level. Otherwise, if therelay K1 is pulled-in during an over high voltage input, the capacitorC5 will be damaged due to overvoltage. If the relay K1 is pulled-inprematurely when the voltage on the capacitor C5 is still at a lowvalue, the surge current will be very large at the moment of pull-in,and a soft start-up will not be implemented.

The input voltage acquisition circuit 2 further includes: a thirdresistor R6, a fourth resistor R7 and a third capacitor C9, wherein oneend of the third capacitor C9 is connected to the PFC circuit 4 and theother end thereof is connected to the MCU chip 5 through the thirdresistor R6 and the third capacitor C9.

In this case, when the input voltage is within a safe range, the MCUchip 5 controls the PFC circuit 4 to be switched on, and when the inputvoltage is out of the safe range, the MCU chip 5 controls the PFCcircuit 4 to be switched off. Thus, power consumption is minimized tosatisfy a standby power consumption of less than 1 W.

The pull-in circuit 3 for the relay K1 is connected to the relay K1 inthe power input circuit 1, the pull-in circuit 3 is configured tocontrol the pull-in of the relay K1 under the control of the MCU chip 5.Specifically, the pull-in circuit 3 for the relay K1 includes a triodeQ2, a fifth resistor R1, a sixth resistor R2 and a fourth capacitor C8,wherein a collector of the triode Q2 is connected to the relay K1, andthe collector and an emitter of the triode Q2 are electrically connectedto the MCU chip 5 through the fifth resistor R1, the sixth resistor R2and the fourth capacitor C8.

The MCU chip 5 is configured to control the PFC circuit 4 to be switchedon and off according to voltage values input by the input voltageacquisition circuit 2, and control the pull-in and drop-out of the relayK1 through the pull-in circuit 3 for the relay K1.

Specifically, the MCU chip 5 is provided with a first input pin INAC anda second input pin INDC which are connected to the input voltageacquisition circuit 2, and is also provided with a first output pin K1ONand a second output pin PFCOFF which are connected to the pull-incircuit 3 for the relay K1 and the PFC circuit 4 respectively.

Hence, the first input pin INAC detects the input voltage, sends apull-in signal to relay K1 through the first output pin KION afterperforming an AD conversion and judgement, and drop out the relay K1 incase of any abnormality. When the relay K1 is dropped-out, the currentis only supplied to a power supply module for a subsequent stage throughthe thermistor PTC in order to secure a standby, therefore such timesequence of pull-in of the relay K1 can effectively suppress an inputinrush current. The relay K1 is pulled-in only when the MCU chip 5detects that an electrolytic capacitor is charged and a certaincondition is met, thereby not only reducing the duration of appliedsurge current, but also reducing a peak in the applied surge current,the switching capacity needed in power distribution and the surgeinterference from the grid. Further, an output signal of the secondoutput pin PFCOFF can switch off the PFC circuit and a subsequent stagethereafter, so as to minimize power consumption, in order to satisfy astandby power consumption of less than 1 W. In one embodiment, the modelof the MCU chip 5 is PIC16F1716-I/SS.

In addition, the MCU chip 5 is also provided with an LED indicatorinterface which can indicate a detection result effectively. By settinga lower and upper limit for a protection voltage and a safe workingvoltage, the MCU chip 5 can indicate overvoltage, phase loss, lowvoltage, lightning and other states with different LED flickers, thusfacilitating maintenance by customers and reducing potential electricshock hazards.

The input detection and protection circuit further includes a powersupply module 6 that supplies power to the relay K1 and MCU chip 5. Thepower supply module 6 does not use a high-voltage electrolytic capacitorsuch that stability of the power supply module 6 is greatly increased.The power supply module 6 can output voltages of 15V and 5V to provideworking voltages respectively to the relay K1 and the chip.

It will be understood by those skilled in the art that the principle,circuit configuration and technical effects of the input detection andprotection circuit according to the present disclosure can be applied tovarious electronic device such as an AC electronic ballast including theinput detection and protection circuit as described above.

In summary, the input detection and protection circuit according to thepresent disclosure can provide protection against abnormalities due toextremely high input voltage, such as phase loss from the grid,incorrect wire connection during installation, high surge voltage at themoment of switching on, impulses by continuous lightning. According tothe present disclosure, the input detection and protection circuitacquires a charging voltage of a capacitor of a subsequent stage, andenables the pull-in of the relay according to the internal setting inorder to effectively reduce surge current and impact. Meanwhile, theinput detection and protection circuit monitors the input voltage, suchthat protection can be provided when the voltage is extremely high orlow, wherein the relay can be dropped-out in case of an abnormality, anda standby current can be provided to the MCU by PTC to indicate suchabnormality.

It will be apparent to a person of ordinary skill in the art that thepresent disclosure is not limited to the details of the exemplaryembodiments described above, but can be embodied in other specific formswithout departing from the spirit or essential characteristics thereof.Therefore, the embodiments shall be in all respects regarded asexemplary and non-limiting, and the scope of the present disclosure isdefined by the appended claims rather than the above description, so itis intended to include all changes that fall within the meaning andscope of equivalent elements of the claims in the present disclosure.Any reference numerals in the claims shall not be taken as limiting theclaims in which they involve.

In addition, it should be understood that although this specification isdescribed in terms of embodiments, however it should not be consideredthat each embodiment contains one independent technical scheme. Thisdescription of the specification is merely for clarity. A person ofordinary skill in the art shall take the specification as a whole, andthe technical schemes in each embodiment can be appropriately combinedto form other embodiments that can be understood by a person of ordinaryskill in the art.

The invention claimed is:
 1. An input detection and protection circuit,wherein the input detection and protection circuit comprising: a powerinput circuit, wherein the power input circuit performs a firstlimitation to an input surge voltage, and then performs a secondlimitation to a residual voltage from the first input surge voltagelimitation; an input voltage acquisition circuit, wherein the inputvoltage acquisition circuit feeds back an input voltage to an MCU chipof the input detection and protection circuit; a pull-in circuit for arelay, wherein the pull-in circuit for the relay is connected to therelay in the power input circuit; and a PFC circuit, wherein the MCUchip controls the PFC circuit to switch on and off according to voltagevalues input by the input voltage acquisition circuit, and controlspull-in and drop-out of the relay through the pull-in circuit for therelay; and the power input circuit comprises: a first varistor, a secondvaristor, a thermistor and the relay, and wherein the input surgevoltage is firstly limited by the first varistor and then secondlylimited by the second varistor and the thermistor.
 2. The inputdetection and protection circuit according to claim 1, wherein the powerinput circuit further comprises a third varistor connected in parallelto both ends of the thermistor.
 3. The input detection and protectioncircuit according to claim 1, wherein the input voltage acquisitioncircuit comprises: a first diode, a second diode, a first capacitor, asecond capacitor, a first resistor and a second resistor; and whereinone end of each of the first and second diodes is connected to the powerinput circuit and the other end thereof is connected to the MCU chipthrough the first and second capacitors and the first and secondresistors.
 4. The input detection and protection circuit according toclaim 3, wherein when the input voltage is within a certain safe range,the MCU chip controls the pull-in of the relay through the pull-incircuit for the relay, and when the input voltage is out of the saferange, the relay is dropped-out.
 5. The input detection and protectioncircuit according to claim 1, wherein when the input voltage is within acertain safe range, the MCU chip controls the pull-in of the relaythrough the pull-in circuit for the relay, and when the input voltage isout of the safe range, the relay is dropped-out.
 6. The input detectionand protection circuit according to claim 5, wherein when the inputvoltage is within the certain safe range, the MCU chip controls the PFCcircuit to be switched on, and when the input voltage is out the saferange, the MCU chip controls the PFC circuit to be switched off.
 7. Theinput detection and protection circuit according to claim 1, wherein theinput voltage acquisition circuit comprises: a third resistor, a fourthresistor and a third capacitor; and wherein one end of the thirdcapacitor is connected to the PFC circuit and the other end thereof isconnected to the MCU chip through the third resistor and the thirdcapacitor.
 8. The input detection and protection circuit according toclaim 1, wherein when the input voltage is within a certain safe range,the MCU chip controls the PFC circuit to be switched on, and when theinput voltage is out the safe range, the MCU chip controls the PFCcircuit to be switched off.
 9. The input detection and protectioncircuit according to claim 1, wherein the pull-in circuit for the relayincludes a triode, a fifth resistor, a sixth resistor and a fourthcapacitor, a collector of the triode is connected to the relay, and thecollector and an emitter of the triode are electrically connected to theMCU chip through the fifth resistor, the sixth resistor and the fourthcapacitor.
 10. The input detection and protection circuit according toclaim 1, wherein the input detection and protection circuit furtherincludes a power supply module that supplies power to the relay and theMCU chip.